The EvIo class

(PECL ev >= 0.2.0)

Introduzione

EvIo
watchers check whether a file descriptor(or socket, or a stream castable
to numeric file descriptor) is readable or writable in each iteration of
the event loop, or, more precisely, when reading would not block the
process and writing would at least be able to write some data. This
behaviour is called
level-triggering
because events are kept receiving as long as the condition persists. To
stop receiving events just stop the watcher.

The number of read and/or write event watchers per
fd
is unlimited. Setting all file descriptors to non-blocking mode is also
usually a good idea(but not required).

Another thing to watch out for is that it is quite easy to receive false
readiness notifications, i.e. the callback might be called with
Ev::READ
but a subsequent
read()
will actually block because there is no data. It is very easy to get into
this situation. Thus it is best to always use non-blocking I/O: An extra
read()
returning
EAGAIN
(or similar) is far preferable to a program hanging until some data
arrives.

If for some reason it is impossible to run the
fd
in non-blocking mode, then separately re-test whether a file descriptor is
really ready. Some people additionally use
SIGALRM
and an interval timer, just to be sure thry won't block infinitely.